Compasses

ABSTRACT

Improved compasses consisting of two arms adapted to be locked in adjustable angular positions and of a scriber arranged at the intersection of the useful edges of these arms; a circle is drawn by placing the compasses on the sheet and causing it to slide in such a manner that the straight edges of the arms pass at all times through two fixed points.

United States Patent [1 1 Debeaux Jan. 1,1974

[ COMPASSES [76] Inventor: Pierre Debeaux, 2 Boulevard dArcole,Toulouse-Haute-Garonne, France [22] Filed: Mar. 22, 1972 [2 1] Appl.No.: 236,906

[52] U.S. Cl. 33/27 F [51] Int. Cl B431 9/00 [58] Field of Search 33/27F [56] References Cited UNITED STATES PATENTS 593,236 11/1897 Noyes33/27 F 2,552,215

5/1951 Rekdahl 33/27 F FOREIGN PATENTS OR APPLICATIONS 84,778 8/1920Switzerland 33/27 F 13,619 10/1903 Austria 33/27 F PrimaryExaminer-Harry N. Haroian Attorney-Roger Goudreau 5 Claims, 5 DrawingFigures PATENTED 1 I974 SHEET 1 OF 2 FIG/1 COMPASSES The inventionrelates to improved compasses for use in drawing circumferences,especially circumferences of large diameter or circumferencespassingthrough three given points. The invention relates also to amethod of using such compasses.

Conventional compasses consist of two moving arms hinged to each other,with means for locking the arms to each other in a desired relativeposition However, if such compasses are tobe of reasonable dimensions,they cannot be used for drawing parts of circumferences having large orvery large diameters. Moreover, it is impossible with compasses of thiskind to draw a circumference passing through three given points, withoutprior geometrical construction.

it is an object of the present invention to provide improved compasses,especially with a view to overcoming the foregoing deficiencies ofconventional compasses; to this end, the compasses comprise two movingarms, hinged to each other, and means for locking the arms to each otherin a desired relative position. Each arm consists of a relatively flatrulerhaving. an edge which is scrupulously straight over a specificuseful length. The compasses further comprise, in the area where therulers are hinged to each other, means for locating and locking ascriber, such as a pencil or bowpen, the means designed to hold thescriber and to cause the marking end thereof to coincidewith theimaginary intersection of two straight lines extending the two straightedges mentioned above, regardless of the position of the two rulers.

A method of using compasses of this kind for the purpose for example ofdrawing on a plane surface a circumference passing through three givenpoints, involves the following operations:

laying the compasseson the flat surface;

arranging the two rulers thereof in such a manner that two of the pointsare each located on one of the straight edges of the two rulers;

altering the angle between the rulers, while still keeping the straightedges on the two points, in order to bring the marking element of thescriber to the third point;

locking the two rulers together inthis position with the aid of thelocking means; and

causing the compasses to slide, making sure that the straight edges ofthe rulers pass respectively through the two points.

The marking element of the compasses then traces, on the plane surface,a circumference, since the apex of a fixed angle (the sides of whichpass through two given fixed points) lies on the arc of'a circle. Itshould be noted that the radii of circles drawn with such compasses maybe as large as may be desired, since the angle between the two rulersmay be as much as 180, in which case the straight edges of the tworulers are in alignment and the curve drawn is a straight line (acircumference having a radius of infinite length).

According to one embodiment of the invention, the means for locating andlocking the scriber consist of a holder in which the scriber isfastened, the outside cylindricalsurface of the holder serving as acentre about which the rulers of the device pivot; the axis of theholder is designed to co-operate with the lines extending the straightedges ofthe two rulers. In this way, the marking element of the scribercoincides at all times with the point of intersection of the extensionsof these straight edges, and therefore with the apex of the anglethereby defined; this is the condition required in order that themarking element shall draw a circumference. The present embodiment ofthe invention has the advantage of being an extremely simple structure.

According to another embodiment of the invention, the means for locatingthe scriber consist of a guide strip at the end of which are located themeans of holding the scriber. This strip is held and guided:

on the one hand, by at least one guide pin running in a slot in thestrip which is linked to the rulers in such a manner that it is causedto pass vertically above the hinge point of the two rulers; and

on the other hand, by a stud carried on the strip, the

stud engaging in two intersecting slots curving in the form of aconchoid, one curve being arranged in each of the rulers, and one curvebeing superimposed on the other.

The straight line considered for the above-mentioned conchoidal curveconsists, for each ruler, of the straight edge thereof and itsextension, whereas the fixed point of the conchoid is merged with thehinge point of the rulers. The means for holding the scriber is attachedto the guide strip in such a manner that the marking element thereof islocated on the imaginary lines extending the straight edges of the tworulers. As will be explained hereinafter in connection with the drawingsattached thereto, as a result of the properties of conchoidal curves,the marking element is caused to coincide at all times with the point ofintersection of the straight edges of the two rulers.

The part of each ruler overlapping, or capable of overlapping, theequivalent part of the other ruler may, with advantage have anindentation at the end of the straight edge, in order that the user ofthe device may have a direct view of the line he is drawing.

Furthermore, the guide pin of the guide strip may with advantage consistof a centre about which the rulers are hinged. This guide pin may alsobe in the form of a pin carried by two arms, one end of each of whichpivots about the pin, while the other end of each arm is hinged to oneof the rulers.

The compasses according to this second embodiment may also be providedwith two guide pins on the guide strip, engaging with two slots therein:the one being the centre about which the rulers are hinged, while theother is a pin carried by two arms, one end of each of these armspivoting about the pin, while the other end of each arm is hinged to oneof the rulers. This provides stronger and more accurate guidance of thestrip.

The means used for locking the rulers may be a nut, especially awing-nut screwed to the pin about which the rulers are hinged, a certainlength of the pin being threaded.

The invention also covers the method for using the compasses describedabove. This method may be facilitated by sticking two pins into thepoints through'which the straight edges of the rulers must pass, thecompasses being then slid with the straight edges resting against thepins.

The invention will be better understood with the aid of the followingdetailed description and the drawings attached hereto which illustratetwo embodiments thereof. In these drawings:

FIG. 1 shows a perspective view of a first embodiment of the compassesmade in accordance with the invention;

FIG. 2 shows a top view of a second embodiment thereof;

FIG. 3 is a detail showing how to construct the conchoidal curves on therulers, which curves will make it possible to produce slots therein;

FIG. 4 illustrates schematically a method of using the compasses shownin FIG. 2;

FIG. 5 is a geometrical figure making it possible to justify the methoduse shown in FIG. 4.

The compasses (FIG. 1) consist of two flat rulers 1 and 2 hinged to eachother at a widened part 3 located at one end of each ruler. Each ofthese rulers is provided at 4,4 with a scrupulously straight edge over aspecific useful length.

The two rulers 1, 2 are hinged together by means of a holder 5 in thehollow core of which a scriber, such as a pencil 6, may be fastened. Theaxis of this holder is perpendicular to the plane of rulers 1,2, and islocated, in this plane, at the intersection of the extensions (shown indotted lines in FIG. 1) of straight edges 4 and 4. The lead in pencil 6thus coincides with the point of intersection of these extensions.

Furthermore, one of the rulers is provided with a slot 7 accommodating aheaded screw 8 which makes it possible to pivot an arm 9 also providedwith a slot 10. One end of this arm 9 is hinged at 11 to the other rulerl. A wing nut 12 may be tightened on to screw 8 for the purpose oflocking arm 9 in a particular position; it will be understood thatlocking this arm in a given position locks rulers 1,2 together at aspecific relative angle to each other.

In a second embodiment of the invention (see FIG. 2), there are tworulers 13,14, each of which is provided with a scrupulously straightedge, as at 15,15, over a specific useful length. These rulers arehinged to each other by means of a headed screw, the end of which may beseen at 16; this screw runs in slots arranged in the rulers at aspecific distance from the ends thereof and from straight edges and 15'.An indentation 17 is arranged at the end of each of these straightedges, mainly in the parts of the rulers adapted to overlap.

Moreover, a holder 18 is fixed at the end of a guide strip 19 toaccommodate the scriber, such as a pencil or a bowpen (not shown in FIG.2). This strip 19 has two slots, one marked 20 accommodating a headedscrew 16, the other marked 21 accommodating a headed screw 22 of smallerdiameter. This screw 22 hinges to guide strip 19 two arms 23,24, theother ends of which are hinged to rulers 13,14 respectively.

Rulers 13,14 are also provided with identical slots, as at 25, the slotscrossing and accommodating a stud 26; the latter is attached to guidestrip 19 and assists in guiding it.

Finally, a wing-nut 27 on screw 16 makes it possible to lock ruler 13,ruler 14, and guide strip 19 into an immovable whole; when this screw isloosened, however, rulers 13,14 may pivot about screw 16, at which timeguide strip 19 is guided by its stud 26 running in slot 25, by screw 16running in slot 20, and by screw 22 running in slot 21. It should benoted that the two latter elements act similarly upon this guide piece,and that one of them could be eliminated; however, the provision of twoelements produces better guidance.

Since arms 23,24 are equal in length and are hinged symmetrically torulers 13,14, guide strip 19 is forced to remain on the bisector of theangle between rulers 13,14. Stud 26, running in identical slots 25 inthe rulers, determines the location of guide strip 19 on this bisector.Details of the shape of slots 25 will be given below.

The purpose of these slots is to ensure that the axis of holder 18 shallat all times be vertically above the point of intersection of theextensions (shown in dotted lines in FIG. 2) of straight edges 15 and15; these slots are arranged on either side of curves describedhereinafter and wide enough to accommodate, with a certain amount ofplay, stud 26. The curves are conchoids, a diagram for the constructionthereof being given in FIG. 3.

This figure illustrates schematically ruler 13 with its straight edge15; point 1 represents the hinge point about which the rulers pivot;regardless of the position of the axis of strip 19, for example alongIG, IF, IE or ID, the axis of holder 18 must lie along the extension ofstraight edge 15 and therefore, in the examples selected, at G, F, E, orD. Since stud 26 and holder 18 are integral with guide strip 19, thedistance between the axis of the holder and that of the stud isconstant. All that is required, therefore, is to transfer to straightlines IG, IF, IE, ID, from points G, F, E or D, distances GG FF EE DDwhich are equal to the distance between the centre of the stud and theaxis of the holder. The position of the centre of the stud, passingthrough points G, F, E and D, thus determines the position of the axisof holder 18 on the extension of straight edge 15; a curve of this kindis known to mathematicians as a conchoid. Thus by producing a slot oneither side of conchoidal curve D, G, which will accommodate stud 26,the axis of holder 18, and therefore the lead of the marking pencil,will rest upon the extension of straight edge 15 of ruler 13; if anidentical slot is produced in ruler 14, and stud 26 is similarly engagedtherewith, guide piece 19 will be held in such a manner that the lead ofthe marking pencil will lie at the same time on both extensions of thestraight edges of rulers 13 and 14, and will therefore coincide with thepoint of intersection of these extensions.

The structure of the second embodiment is slightly more complex thanthat of the first embodiment; however, it has the additional advantageof providing the user with a direct view of the line he is drawing,since indentations 17 ensure that there is nothing to hide the line inthe vicinity of pencil-holder 18.

FIG. 4 illustrates schematically how the compasses according to theinvention are used. In the example shown in this figure, it is desiredto draw a circumference having a large radius and passing through threegiven points AB and C. The draughtsman has located a pin at each'ofpoints A and B, be has loosened wingnut 27 and has placed the lead ofthe pencil on point C, keeping the straight edges of the rulers againstpins 28,29. He now locks rulers 13,14 and guide piece 19 by tighteningwing-nut 27; all he now has to do is to slide the compasses on the planesurface, keeping the straight edges of rulers 13,14 against pins 28,29.Two positions of the compasses corresponding to points C and C have beenindicated in FIG. 4.

It will now be demonstrated, with reference to FIG. 5, that the curvedrawn by the lead of the pencil is a circle passing through points ABand C. Now, regardless of the position of the compasses, angle ACB (orAC'B or AC"B) is constant, since rulers 13,14 are locked together. it isknown that the apex of a constant angle, whose sides pass through twofixed points, lies on a circumference. v

The main interest of the compasses according to the invention is that,on the one hand, it is possible to draw a circumference passing throughthree given points without any geometrical construction and, on theother hand, that it is possible to draw circumferences of very largeradius, since the limiting position of rulers 13,14 is when they arealigned with each other.

What I claim is:

l. Compasses for drawing arcs comprising: two movable arms hinged at onepoint to each other; means for locking said arms to each other; eachsaid arm including a substantially fiat ruler having a straight edgeextending over a given length; the straight edges of said rulersdefining straight lines extending to an imaginary point of intersection;said rulers having overlapping parts; means for holding a scriber means;a guide strip disposed at the hinge point of said arms for positioningsaid scriber means; said means for holding the scriber means beinglocated at one end of the guide strip; said guide being retained andguided by at least one guide pin accommodated in a slot in said guidestrip and being connected to the rulers whereby said guide strip passesvertically above the hinge point of said rulers; said guide strip beingfurther retained and guided by a stud integral with said guide strip andrunning in two intersecting slots which follow a curve in the form of aconchoid, said slots being arranged in said overlapping parts of therulers, the straight line considered by the conchoid being the straightline of each ruler, whereas the fixed point of the conchoid merges withthe hinge point of the rulers, said means for holding the scriber meansbeing attached to the guide strip in such a manner that the scribermeans is located on the imaginary point of intersection of said straightlines.

2. Compasses according to claim 1, wherein the overlapping part of eachruler, has an indentation at the end of the straight edge with whichsaid ruler is provided.

3. Compasses according to claim 1, wherein the axis of the guide stripis the axis about which the rulers are hinged.

4. Compasses according to claim 1, wherein the guide pin of the guidestrip is carried on two arms, one end of each arm being hinged aboutsaid pin, the other end of each arm being hinged to one of the rulers.

5. Compasses according to claim 1, wherein the guide strip has two guidepins running in two slots therein, one being the axis about which therulers are hinged, and the other being a pin carried on two arms, oneend of each arm being hinged about said pin, and the other end of eacharm being hinged to one of the rulers.

1. Compasses for drawing arcs comprising: two movable arms hinged at onepoint to each other; means for locking said arms to each other; eachsaid arm including a substantially flat ruler having a straight edgeextending over a given length; the straight edges of said rulersdefining straight lines extending to an imaginary point of intersection;said rulers having overlapping parts; means for holding a scriber means;a guide strip disposed at the hinge point of said arms for positioningsaid scriber means; said means for holding the scriber means beinglocated at one end of the guide strip; said guide strip being retainedand guided by at least one guide pin accommodated in a slot in saidguide strip and being connected to the rulers whereby said guide strippasses vertically above the hinge point of said rulers; said guide stripbeing further retained and guided by a stud integral with said guidestrip and running in two intersecting slots which follow a curve in tHeform of a conchoid, said slots being arranged in said overlapping partsof the rulers, the straight line considered by the conchoid being thestraight line of each ruler, whereas the fixed point of the conchoidmerges with the hinge point of the rulers, said means for holding thescriber means being attached to the guide strip in such a manner thatthe scriber means is located on the imaginary point of intersection ofsaid straight lines.
 2. Compasses according to claim 1, wherein theoverlapping part of each ruler, has an indentation at the end of thestraight edge with which said ruler is provided.
 3. Compasses accordingto claim 1, wherein the axis of the guide strip is the axis about whichthe rulers are hinged.
 4. Compasses according to claim 1, wherein theguide pin of the guide strip is carried on two arms, one end of each armbeing hinged about said pin, the other end of each arm being hinged toone of the rulers.
 5. Compasses according to claim 1, wherein the guidestrip has two guide pins running in two slots therein, one being theaxis about which the rulers are hinged, and the other being a pincarried on two arms, one end of each arm being hinged about said pin,and the other end of each arm being hinged to one of the rulers.